/Engine/Source/Runtime/SlateCore/Public/Rendering/SlateRenderer.h
Sets fullscreen state on the window's rendering viewport
void UpdateFullscreenState ( const [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWindow](API\Runtime\SlateCore\Widgets\SWindow) > InWindow, uint32 OverrideResX, uint32 OverrideResY )